Error in documentation for 'made up keys' in Song Objects section

[aaronlutze]

Issue description

The word 'data-' is missing from the example to display custom data types from the song info object in the support documentation.

<span class="made-up-key" amplitude-song-info="made_up_key">

Environment

All

Steps to reproduce the issue

1. Add a made up key to the song object
2. To render the value of the made up key in your app, use the supplied code example from the docs of
   <span class="made-up-key" amplitude-song-info="made_up_key">
3. Note that it doesn't render.

What is expected?

You need to add data- before amplitude-song-info in order to render.
<span class="made-up-key" **data-amplitude-song-info**="made_up_key"></span>

Link to where issue can be reproduced

https://521dimensions.com/open-source/amplitudejs/docs/configuration/song-objects.html#special-keys